Golf ball cores having foam center and polymeric outer layers with hardness gradients

Abstract

Multi-layered golf ball core sub-assemblies and the resulting golf balls are provided. The core structure includes an inner core (center) comprising a foam composition, preferably foamed polyurethane. The intermediate core layer is preferably formed from a thermoplastic composition such as an ethylene acid copolymer ionomer resin; and the outer core layer is preferably formed from a thermoset composition such as polybutadiene rubber. The core layers have different hardness and specific gravity levels. The core assembly preferably has a positive hardness gradient extending across the entire assembly. The core structure and resulting ball have relatively good resiliency.

We claim:  
     
       1. A core assembly for a golf ball, comprising:
 i) an inner core layer comprising a foamed composition, the inner core layer having a diameter in the range of about 0.100 to about 1.100 inches, a specific gravity (SG inner ), and an outer surface hardness (H inner core surface ) and a center hardness (H inner core center ), the H inner core surface  being greater than the H inner core center  to provide a positive hardness gradient; 
 ii) an intermediate core layer comprising thermoplastic, material, the intermediate layer being disposed about the inner core and having a thickness in the range of about 0.050 to about 0.400 inches, a specific gravity (SG intermediate ), and an outer surface hardness (H outer surface of IC ) and an inner surface hardness (H inner surface of IC ), the H outer surface of IC  being the said or less than the H inner surface of IC  to provide a zero or negative hardness gradient; and 
 iii) an outer core layer comprising a thermoset material, the outer core layer being disposed about the intermediate core layer and having a thickness in the range of about 0.200 to about 0.750 inches, a specific gravity (SG outer ), and an outer surface hardness (H outer surface of OC ) and an inner surface hardness (H inner surface of OC ), the H outer surface of OC  being greater than the H inner surface of OC  to provide a positive hardness gradient, 
 wherein the SG outer , is greater than the SG inner , and the SG intermediate  is greater than the SG inner , and the center hardness of the inner core (H inner core center ) is in the range of about 10 shore C to about 60 Shore C and the outer surface hardness of the outer core layer (H outer surface of OC ) is in the range of about 40 Shore C to about 93 Shore C to provide a positive hardness gradient across the core assembly. 
 
     
     
       2. The core assembly of  claim 1 , wherein the inner core comprises a foamed polyurethane composition. 
     
     
       3. The core assembly of  claim 2 , wherein the foamed polyurethane composition is prepared by adding water to a mixture of polyisocyanate, polyol, and curing agent compounds, surfactant and catalyst, the water being added in a sufficient amount to cause the mixture to foam. 
     
     
       4. The core assembly of  claim 1 , wherein the intermediate core layer comprises at least one thermoplastic material selected from the group consisting of partially-neutralized ionomers; highly-neutralized ionomers; polyesters; polyamides; polyamide-ethers, polyamide-esters; polyurethanes, polyureas; fluoropolymers; polystyrenes; polypropylenes; polyethylenes; polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinyl alcohols; polyester-ethers; polyethers; polyimides, polyetherketones, polyamideimides; and mixtures thereof. 
     
     
       5. The core assembly of  claim 4 , wherein the thermoplastic material is a highly-neutralized ionomer composition comprising an E/X/Y-type copolymer, wherein E is ethylene, X is a C 3 -C 8  α,β-ethylenically unsaturated carboxylic acid present in an amount of 10 to 20 wt. %, based on total weight of the copolymer, and Y is an acrylate selected from alkyl acrylates and aryl acrylates present in an amount of 0 to 50 wt. %, based on total weight of the copolymer, wherein greater than 70% of the acid groups present in the composition are neutralized with a metal ion. 
     
     
       6. The core assembly of  claim 1 , wherein the outer core layer comprises at least one thermoset rubber material selected from the group consisting of polybutadiene, ethylene-propylene rubber, ethylene-propylene-diene rubber, polyisoprene, styrene-butadiene rubber, polyalkenamers, butyl rubber, halobutyl rubber, polystyrene elastomers, copolymers of isobutylene and p-alkylstyrene, halogenated copolymers of isobutylene and p-alkylstyrene, copolymers of butadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber, and mixtures thereof. 
     
     
       7. The core assembly of  claim 1 , wherein the inner core has a diameter in the range of about 0.100 to about 0.800 inches and specific gravity in the range of about 0.25 to about 0.95 g/cc; and wherein the H inner core center  is in the range of about 10 Shore C to about 50 Shore C and the H inner core surface  is in the range of about 13 Shore C to about 60 Shore C. 
     
     
       8. The core assembly of  claim 1 , wherein the H inter surface of IC  is in the range of about 35 Shore C to about 96 Shore C, and the H outer surface of IC  is in the range of about 32 Shore C to and about 93 Shore C. 
     
     
       9. The core assembly of  claim 1 , wherein the outer core layer has a thickness in the range of about 0.150 to about 0.650 inches and specific gravity in the range of about 0.90 to about 2.90 g/cc; and wherein the H inner surface of OC  is in the range of about 40 Shore C to about 87 Shore C and the H outer surface of OC  is in the range of about 43 Shore C to about 90 Shore C. 
     
     
       10. The core assembly of  claim 1 , wherein the H inner core center  is in the range of about 13 Shore C to about 55 Shore C and the H outer surface of OC  is in the range of about 43 Shore C to about 87 Shore C to provide a positive hardness gradient across the core assembly.